CaF₂ and CaSO₄ in white cement clinker production

A review of the fluxing and mineralizing effects of CaF₂ and CaSO₄ during the clinkering process is presented. The simultaneous addition of CaSO₄ and CaF₂ to compositions in the system CaO—Al₂O₃—Fe₂O₂-SiO₂ results in formation of phases not found in ordinary Portland cement: for example, C₁₁A₇·CaF₂, C₄A₃S, and 3C₂S·3CaSO₄·CaF₂, etc. These modify the compatible equilibrium phases as well as the stable primary fields of C₃A and C₃S. Finally, CaSO₄ and CaF₂ are responsible for changing the melt composition together with its rheological characteristics. Clinkerization of raw meals with silica moduli greater than 10 and lime saturation factor greater than 0·95 is possible when CaF₂ and gypsum partially replace traditional fluxes. Finally, the results of an industrial test in which a mineralized white cement (AS-SR type) was produced are presented. The clinker has about 80% silicates plus aluminates; fluorellestadite is a characteristic phase of this process. The thermal and economic balances are positive compared to traditional fabrication. The durability properties of the new cement, when subject to attack by sulfates and sea water, are much better than a normal white cement.